Well, you _do_ say: "This software is not currently available under any license." I know that's not what you _mean_, but it's what you _say_. My personal and uninformed option is that you should probably change this to something along the lines of: "This software may be studied but not modified, and copies not be redistributed", which is more explicit.

I am not, personally, a fan of the GPL (it makes things too complicated) and tend to release all my software as MIT or BSD-2 because I like the simplicity. But Apache-2 is a perfectly decent license. Nobody will complain about that.

Ah, here's a good bullet-point comparison: http://choosealicense.com/licenses/